Such a lamp, in which the electric element is a pair of electrodes, is known from European Patent Application EP 0 478 058 A1corresponding to U.S. Pat. No. 5,216,319.
The lamp is designed to be used as a light source in optical systems, for example as a vehicle headlamp.
The sleeve and the fixation member are necessary for fixing the lamp vessel to the lamp cap in a position in which the electric element, or in the case of a pair of electrodes the discharge arc between them, is aligned relative to reference locations on the lamp cap. As a result, the electric element is given a predetermined position when the lamp is placed in an optical system. The lamp vessel may be shifted, tilted, and rotated during alignment, as necessary.
It is of major importance for the sleeve to hold on to the lamp vessel securely and nevertheless to cause no damage to the glass. It should be prevented that the sleeve loses its grip in the case of a temperature rise, during lamp operation, owing to a comparatively great thermal expansion, while on the other hand it should be prevented that the sleeve clamps too strongly at normal temperatures, when the lamp is extinguished, and generates undesirable strain in the glass.
It was found that the known sleeve involves the risk of causing damage to the glass it clamps when it is closed through making of welded joints during mechanized manufacture. Premature lamp failure can occur as a result of this. It was also found to be difficult to provide the known sleeve in mechanized manufacture.